Radical new proposal from 58 medical experts would decenter BMI from obesity diagnosis

The way obesity is diagnosed now either leads to ineffective treatments for those who most need it, or unnecessary treatment for those who don’t, says Dr. Francesco Rubino, commission chair and a bariatric surgeon at King’s College Hospital in London. As it stands, obesity diagnoses are mostly used as a “risk assessment,” Rubino says, meaning they reflect probability of risk for other diseases, not the current state of someone’s health.

That assessment stems from another deep flaw Rubino and his colleagues see in obesity treatment: using the ratio of height and weight, or body mass index (BMI). Because obesity is strictly defined as a BMI over 30, he says there are not only patients wrongly diagnosed with obesity, but also a lack of individualized care.

“We need to improve the accuracy of detection of obesity itself,” Rubino tells Fortune. “We know that BMI already is not very good at that.” 

An Olympic athlete could be considered to have obesit, because their body weight is higher from muscle, Rubino says, while another person could have heavier bones. The key is where someone is carrying fat on their body, he says, and how much.

“Obesity is a spectrum. And trying to paint it as only one thing, it really doesn’t work,” Rubino says.

The proposal has been in the works since 2019, and over the course of 600 to 700 meetings, commission members came to a consensus about how to change obesity diagnosis and care. The proposal does not mean the changes are certain to be implemented, but its publication could lead to some of the biggest shifts in obesity treatment, Rubino says. 

Flaws with how obesity is currently diagnosed

According to the World Health Organization (WHO), rates of obesity have more than doubled from 1990 to 2022, jumping from an estimated 7% of adults living with obesity to 16%. Over one billion people worldwide have obesity.

The current treatment usually involves telling patients to alter their lifestyles—increasing diet and exercise—to lose weight. For some, that is enough. But for others, that is not an effective treatment plan, he says.

“We have always approached obesity as a weight problem,” Rubino says. “We always approached obesity as a risk factor and not an illness, so we don’t have that urgency that we have with other chronic diseases.”

The lack of urgency is what inspired one of the biggest proposed changes: two definitions of obesity, with different treatment approaches.

The first is clinical obesity, which Rubino defines as “excess body fat associated with dysfunction of organs.” That might mean heart failure or dysfunction of the lungs or kidneys, he says.

The commission came up with 18 diagnostic criteria for clinical obesity, including:

• Breathlessness caused by effects of obesity on the lungs 
• Obesity-induced heart failure 
• Knee or hip pain, with joint stiffness and reduced range of motion as a direct effect of excess body fat on the joints 
• Certain alterations of bones and joints in children and adolescents limiting movement 
• Other signs and symptoms caused by dysfunction of other organs including kidneys, upper airways, metabolic organs, nervous, urinary and reproductive systems and the lymph system in the lower limbs

Diagnosing someone with clinical obesity means recognizing it as a chronic disease, he says, rather than a risk factor for other illnesses. That paves the way for more effective, personalized interventions that aim to reduce body fat and regain body functions rather than solely focusing on weight loss.

“It’s not enough to tell someone with clinical obesity, ‘I want you to lose about 10% of your weight,’” Rubino says. “It would be futile with someone who has full blown clinical obesity. You’re basically not taking care of the problem.”

The second category is pre-clinical obesity, which is obesity with normal organ function, but acknowledges the increased risk of developing clinical obesity and other diseases, such as including Type 2 diabetes, cardiovascular disease, and certain types of cancer. 

Interventions for pre-clinical obesity would be less intensive and less costly, Rubino says, and with more of a focus on risk reduction. Care might include doctors monitoring weight loss, diet, and exercise to see how effective they are at reducing symptoms. 

The commission proposes using body size or body fat measurements, such as waist-to-hip ratio or bone densitometry scan or DEXA, in addition to BMI to determine clinical versus pre-clinical obesity

These changes could also have a substantial impact on the prescription of anti-obesity drugs in the age of GLP-1s, Rubino says.

Being more explicit about obesity criteria would likely lead to fewer diagnoses of obesity given the more narrow criteria of clinical obesity. That would lead to fewer GLP-1 prescriptions limited to those who need it most, he says, which will ultimately benefit insurance companies and consumers. With an excess amount of prescriptions, Rubino says, “You will discourage coverage.” But limiting the overdiagnosis of obesity could remedy that, he says.

Steering clinicians away from depending just on BMI doesn’t mean doing away with BMI entirely. Rubino acknowledges it can be an effective screening tool, but shouldn’t be used as a diagnostic one.

“It’s not a diagnosis. It was never meant to be a diagnosis,” he says.

But Rubino recognizes that changing how obesity is both diagnosed and treated is going to be an uphill battle. Doctors are used to the convenience and simplicity of BMI, and getting them to move away from it will be challenging.

“We don’t need a simple change,” Rubino says. “We need an overhaul—a radical one.”

More on obesity:

• The 5 biggest weight loss myths that ‘need to die,’ according to an obesity doctor
• This is the best time of day to exercise for people living with obesity, new study shows
• Zepbound vs. Wegovy: New clinical trial says this weight-loss medication sheds more pounds